The present invention relates to a winding control method of a seatbelt retractor having a function of winding up a seatbelt with a motor, and a seatbelt device having the seatbelt retractor.
In a seatbelt retractor, it is necessary to securely wind up an excessively withdrawn portion of a seatbelt until the seatbelt fits an occupant, or to wind up the withdrawn seatbelt until the seatbelt is securely housed in a casing. It is also necessary to reduce unnecessary tightness in chest or the like of an occupant when the occupant wears the seatbelt in a normal state. The seatbelt retractor may utilize an urging force of a single return spring for winding the seatbelt. When the return spring has a small urging force for winding up the seatbelt to reduce a pressure on the chest of the occupant during wearing, the urging force may be too small to properly retract the seatbelt, thereby deteriorating operational and retracting performance. On the other hand, when the return spring has a large urging force for winding up the seatbelt, the occupant may feel tightness in the chest when wearing the belt in a normal state.
In order to solve the problems, Japanese Patent Publication (Kokai) No. 03-552 and Japanese Patent Publication (Kokai) No. 2001-225720 have disclosed a seatbelt retractor for winding up a seatbelt with a motor in addition to an urging force of a return spring.
When a motor is used for winding a seatbelt, there are the following requirements:
(1) It is necessary to stop power supply to the motor (to stop the winding action) when the seat belt is fully wound. Otherwise, electric power of a buttery is unnecessarily consumed for supplying a current to the motor, and the motor needs to avoid overheat due to a high current flowing for a long period of time.
(2) It is necessary to stop power supply to the motor (to stop the winding action) when the seatbelt is caught by something or an occupant tries to withdraw the seatbelt during the winding of the seat belt. Otherwise, electric power of a buttery is unnecessarily consumed for supplying a current to the motor, and the occupant needs to withdraw the seatbelt under a large resistance force, thereby making the occupant unconformable.
In order to solve the problems, in a conventional seatbelt winding control device, a current flowing through a motor is detected. When a value of the detected current exceeds a predetermined value, it is determined that the present state is one of (1) and (2), and power supply to the motor is cut off (to stop the winding action).
However, such a winding control method of the seatbelt retractor has the following problems. In general, when a winding-up speed is controlled to increase stepwise immediately after a command is sent to the motor to wind up a seatbelt, an accelerating current flows in the motor as shown in FIGS. 3(a) and 3(b).
FIG. 3(a) shows a normal winding control. The winding of the seatbelt is started in a state that a constant voltage is applied to the motor. When the seatbelt is fully wound, the motor is stopped as mentioned above. When the current of the motor rapidly increases and exceeds a threshold value at a point A, the voltage applied to the motor becomes zero (FIG. 3(a) shows a state that the voltage is maintained for easy explanation).
When the motor is accelerated just after the voltage is applied to the motor, an accelerating current flows in the motor. Accordingly, the current at a point B exceeds the threshold value, so that a control device controls the voltage applied to the motor to be zero at the point B.
That is, in FIG. 3(a), it is necessary to control the voltage applied to the motor to be zero at the point A where the current flowing through the motor exceeds the threshold value when the load is increased upon fully winding the seatbelt or withdrawing the seatbelt by an occupant. However, when the motor is started, the current also exceeds the threshold value at the point B. Accordingly, the voltage applied to the motor becomes zero, thereby stopping the motor at the point B as well.
In FIG. 3(b), the rotational speed of the motor increases stepwise, so that the accelerating current does not exceed the threshold value when the motor is started. However, a load current for winding up the seatbelt is overlapped at the second acceleration, so that the current including the accelerating current exceeds the threshold value at a point C. Accordingly, the voltage applied to the motor becomes zero, thereby stopping the motor at the point C.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a winding control method of a seatbelt retractor and a seatbelt device having the seatbelt retractor, in which it is possible to prevent a motor from stopping before reaching a predetermined load due to an accelerating current of the motor.
Further objects and advantages of the invention will be apparent from the following description of the invention.